Common rail injection devices are fuel injection devices for internal combustion engines, in which a high-pressure pump compresses the fuel to a high pressure and delivers this fuel, compressed to a high pressure, via a high-pressure line into a high-pressure fuel accumulator which is generally known as a rail. From this rail, injectors are supplied with fuel and inject the fuel, compressed to a high pressure, into the combustion chambers of the respective internal combustion engine. The injectors here act as valves activated electromagnetically or piezo-electrically, via which the fuel is introduced into the combustion chamber.
In order to ensure as dynamic and precise a pressure supply as possible, a common rail injection device has a fuel return system. This comprises a pressure reduction valve connected to the rail, via which surplus fuel can be returned to the fuel tank of the respective vehicle.
With such a high-pressure injection device, the fuel pressure is always regulated to a desired nominal pressure by a control unit. This regulation is achieved by activating a metering unit arranged on the low-pressure side so as to meet demand.
When the internal combustion engine is a four-stroke engine, the cylinders of the engine are offset to each other such that after two crankshaft revolutions, i.e. after 720°, the first cylinder can begin the working cycle again. This offset gives a mean ignition interval. The time period in-between is known as the segment time of the internal combustion engine. The rotation speed and hence also the segment time are determined from the crankshaft signal. The ignition times and the injection itself are recalculated in step with the segment time. The rotation speed gives the mean crankshaft rotation speed in the segment time and is proportional to the inverse of the segment time.
In known high-pressure injection devices, the pressure reduction occurring via the pressure reduction valve takes place in segment synchrony with a segment of the internal combustion engine, within a single engine segment time. Such a segment-synchronous pressure reduction via the pressure reduction valve has the disadvantage that the pressure reduction times are coupled to the engine segment times, and hence limited. For example, for an internal combustion engine with four cylinders, at a rotation speed of 1000 rpm, the pressure reduction time would be limited to less than 30 ms. In this time period, the pressure reduction valve must be opened and closed again in good time before the start of the next engine segment time, in order to avoid an energy transfer from pulse to pulse and hence a loss of control performance. Consequently, with known high-pressure injection devices, within an engine segment time there is always a safety interval from the next pulse, which further limits the time within which the pressure reduction occurring via the pressure reduction valve can take place.